1. Field of the Invention
The present invention relates generally to data transfer, and specifically to data transfer between separated networks operating according to a Fibre Channel protocol.
2. Background Art
Clients who are coupled within a storage area network (SAN) operating according to a Fibre Channel (FC) protocol, such as the FC-PH Fibre Channel protocol, issued by the American National Standards Institute, Washington, D.C., transfer data between themselves in the form of data-frames. Within the SAN, each client is coupled to an FC switch, and the protocol defines the form to which a header of the frame needs to conform. The header comprises a destination address of the client to whom the data-frame is being sent, and a source address of the transmitting client. The protocol requires that each client within the SAN has a unique address.
FIG. 1 is a schematic diagram of an address structure 10 according to the Fibre Channel protocol, as is known in the art. Address structure 10 is formed of three bytes, and is used both as a source and a destination address identification when data is transmitted. A first byte 12 is an identifier of the switch to which the client is coupled. The FC protocol limits the number of switches within a SAN, identified via byte 12, to 239. A second byte 14, having up to 256 values, is a port identifier of the switch. A third byte 16 is an arbitrated loop identifier. A client is coupled either directly to a port of the switch, or via an arbitrated loop. The arbitrated loop enables up to 256 clients to be coupled to one port of the switch, at a cost of reduced bandwidth, since all communication for these clients traverses the one port and since the loop does not support parallel data transfer. Theoretically, the maximum number of clients supported by the FC protocol is in the case that every port of a switch has an arbitrated loop coupled to the port. In this case the maximum number of clients is 239*256*256. However, if arbitrated loops are not used, the maximum number of clients supported by the protocol is 239*256.
In order that a plurality of initially separate Fibre Channel SANs may be coupled together to form a compound network, so that data-frames may be sent from a client in a first SAN to a client in a second SAN, the addresses of all the clients in the coupled SANs must be unique. Thus, ensuring that clients in the coupled SANs have addresses which are unique throughout the combination may require changing existing addresses of clients in at least some of the previously separated SANs. In addition, the total number of FC switches in the compound network is limited to 239.